When repair work is required on vehicles such as the skin of an aircraft, for example, it may be necessary to take into account the size, shape and location of previous damage and/or repairs for optimum repair of the vehicle. Photographs of the previous damage and/or repair may be made but may not be precisely located or sized on the vehicle or may not be useful for future repair planning. During the analysis of a damage/repair site (i.e. a location of interest) it may be desirable to obtain measurement information without contacting the target object. Due to accessibility and/or contact constraints, it may be difficult to reach the location of interest to obtain position measurements; therefore it is advantageous for a local positioning system to be able to take measurements without contacting the target object and from moderate to large distances from the target object. Local positioning systems which have been used to determine the location, shape and size of damage and/or repairs on vehicles, such as skin damage and/or repairs on an aircraft, for example, may utilize acoustic, laser-based, magnetic, RFID, GPS, and motion capture -based systems. A local positioning system such as the Hexamite HX11, for example, may utilize a minimum of four wireless acoustic sensors (and may require line-of-site) to provide 3-D positioning capability of past damage and/or repairs. The sensors may require mounting on the aircraft with the fourth sensor used to generate point data. Also, curvature of any sort on the surface of the aircraft distorts the acoustic path and reduces the precision to the point that this method will not work in many cases.
Laser-based positioning systems may stand off the aircraft structure to take location data on an aircraft, but may suffer from the requirement that the laser beam be directed in a somewhat perpendicular orientation with respect to the surface of the aircraft skin in order to obtain a sufficiently strong reflection to be recorded. 3A lasers may not be sufficiently strong for use beyond a few feet on most colors of paint, and the stronger 3B lasers may require optical shielding for eye safety.
Other laser-based systems, like the ArcSecond® or Leica Geosystems® trackers, require receivers or reflectors placed at locations of interest. In the case of the ArcSecond system, multiple laser emitters must be placed around the work volume, which increases process complexity and data collection effort of the user.
In a similar manner, motion capture (MoCap) systems, like those from Vicon® or Motion Analysis®, Inc., also require the placement of components around the work volume, in this case multiple camera units, and also require the placement of markers on the target object
Magnetic systems, like those from Ascension®, require placement of magnetic sensors and tend to have accuracy problems due to interference from metal.
GPS and active RFID-based systems don't have the necessary resolution, and also require device placement on the target object.
The capability to rapidly tie features on a vehicle such as on the skin of an aircraft (size, shape and location of structural damage or non-destructive evaluation (NDE) associated to structural damage or the repair of previous structural damage), for example, to coordinate systems may be useful in some circumstances. There may be a need in some circumstances to obtain positional and geometric data in order to establish the appropriate repair design and procedure based upon precise history of past repairs on a particular portion of a vehicle and to relate the data to an engineering data set and maintenance database.